Biologic and analytic components of variation of concentration values of selected serum proteins.

The magnitude and statistical significance of the various biologic and analytic sources of variation of the serum concentration values of seven proteins: albumin, alpha1-antitrypsin, transferrin, orosomucoid, IgG, IgM, and IgA, were evaluated in 12 healthy subjects. Blood specimens were obtained at 0800 h, 1100 h, and 1400 h on one particular day. The analytic error was partitioned into pre-instrumental and instrumental components; the biologic variation was separated into inter-subject variation of mean levels and intra-individual within-day variation. The mean levels of the subjects differed significantly for all seven proteins studied. For the group as a whole there were no consistent diurnal variations of significance. However, for all the proteins, except for IgM, significant individual within-day biologic fluctuations were noted. The within-day biologic variation was smaller than the total analytic variation for transferrin, IgG, orosomucoid, and IgM. When the total analytic variation was separated into pre-instrumental and instrumental components, it was found that the pre-instrumental sources of variation were of a relatively greater magnitude for albumin, IgG, IgA, alpha1-antitrypsin, and IgM.